#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    x=2*(k*(k+1)/2)-1
    s=x-2*(k-1)
    su = 0
    for i in range(s,x+1):
        if i%2 == 0:
            pass
        else:
            su = su + i
    return su

if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer